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National Pi Day!

Happy National Pi Day to math enthusiasts everywhere (or anyone that enjoys a good excuse to eat pie)! Whether you’re celebrating for the Pi or Pi(e), let’s dive in to some fun facts and activities that will help you make the most out of this obscure holiday.

1. Challenge Your Friends and Family to a Competition

Pi is an irrational number, which means that it cannot be expressed by a simple fraction. That's because pi is what mathematicians call an "infinite decimal". After the decimal point, the digits go on forever and ever, and does not get to a point where the same set of numbers is repeated over and over. So, although we use approximations such as 3.14 or 22/7, these rational expressions are accurate only to a certain number of decimal places.

You can find the first million digits of pi here. Spend the day trying to learn as many digits of pi as you can, and then test your memory! Need some insPIration? According to the Pi World Ranking List, the record for reciting the most digits of pi belongs to Suresh Kumar Sharma of India, who recited pi to a whopping 70,030 decimal places in 2015! 2. Find Your Birthday in Pi

March 14th happens to be Albert Einstein’s birthday. Coincidence? Mathematicians estimate that it would take 133 years for a person to recite the first 6.4 billion digits of pi without stopping, and that doesn't include the calculations. Thankfully, we have computers that can calculate for us. In fact, a supercomputer in Switzerland was recently able to calculate 62.8 trillion digits in just 108 days! While I am sure there are more mathematically practical uses for expanding pi, here is a fun app that searches pi for your birthdate. You can even share your results on social media.

3. Explore the Proof of Pi Pi (π) is the ratio of any circle’s circumference to its diameter. The value of this ratio is approximately 3.14 (hence the date), and applies to any circle, big or small. The concept of pi has been around since ancient Babylon and Egypt, and over time, has become more precise. So, just how can we go about proving that the ratio of any circle’s circumference to its diameter does, in fact, give us pi? Try this: All you need is something circular (like a paper plate), string that isn’t too stretchy, and scissors.

Step 1: Measure the string around the edge of the circular object. Cut it to the size of the circumference.

Step 2: Measure the string across the diameter of the circular object, and cut it to length (do this 3 times).

Step 3: Line up the strings to see how many diameter-length strings make up the circumference-length string.

Regardless of the size of the circle or the object chosen, the circumference will always equal a little more than three times the diameter. This value is π. Pretty neat! Therefore, to find the circumference of a circle, we simply multiply the diameter times π. Or more commonly, we multiply two radiuses by π (since the radius is half the diameter), or 2πr. If you’re still confused, check out this video!

For those wanting to take it a step further, in addition to the circumference of a circle, pi is also related to the area, using the formula πr², where r is a circle’s radius (half the diameter). Below you will find one of my favorite explanations of why this works!

First, we slice up a circle and rearrange the pieces. In the example above, the circle is divided into 16 equal pieces. Then, we take one piece off the end, and cut it in half, and move it to the other side. Notice the final figure resembles a rectangle! Visually, we can see that the circumference of the original circle now makes up the top and bottom of the “rectangle”, so the length of the rectangle would be equal to half of the circumference. We already proved that the circumference is 2πr, so half of that would simply be πr. Furthermore, we can see the width of the “rectangle” is equal to the radius, r. Lastly, we know that the area of a rectangle is length times width. In the case of our rectangle above, that’s πr times r, or πr². While this isn’t a completely accurate explanation for why the area of the original circle is πr², since the rectangle isn’t exactly a rectangle, it’s pretty close and gives a good explanation for why the formula is true. Plus, the smaller the slices, the more rectangular it will look! 4. Read a Pi-Themed Book When I was teaching fifth grade, a colleague referred me to Sir Cumference and the Dragon of Pi. It is an engaging tale that introduces and explains the concept of pi, full of delightful mathematical wordplay. It is one of the more well-known books that explores the incredible number. However, there are some other books about pi that are equally good reads. Below are a few more to check out:

Happy Pi Day to You! Another great children's book for exploring pi. Part of the Cat in the Hat Learning Library, the Cat in the Hat demonstrates how to measure a circle's circumference and diameter, and to use those measurements to calculate pi, using various household objects such as a can and string. The Joy of Pi This is the perfect book for an older audience that makes it easy and fun to learn about pi. It also contains one million digits of pi in the tiniest, tiniest print and pretty much everything you want to know, or didn’t know that you wanted to know, about pi. Not A Wake I actually haven’t read this book, but I am fascinated by the unique premise! If you check it out, you’ll have to let me know what you think. Basically, it is literally 10,000 digits of pi, converted into words of the length of each successive digit, across an entire book of poems and short stories. 5. Enjoy Some Delicious Pi(e)

image source: Okay, fine. Pi Day just wouldn’t be Pi Day without indulging in some yummy dessert. In fact, the first National Pi Day was observed in 1988 by American artist and physicist Larry Shaw, who marched around in circles with his colleagues and snacked on various kinds of pie. So, put on your apron or head to your local bakery, and enjoy a delicious slice of math! My kids and I like adding a bit of extra nerdsauce on top by taking the first bite at 1:59pm. You know, because 3.14159… So, how will you be celebrating National Pi Day? Tell me in the comments!

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